Do not use torch.float64 on the mps device (huggingface#942)

* Add failing test for huggingface#940.

* Do not use torch.float64 in mps.

* style

* Temporarily skip add_noise for IPNDMScheduler.

Until huggingface#990 is addressed.

Author: pcuenca

schedulers/scheduling_lms_discrete.py

@@ -252,7 +252,8 @@ def add_noise(
     ) -> torch.FloatTensor:
         # Make sure sigmas and timesteps have the same device and dtype as original_samples
         self.sigmas = self.sigmas.to(device=original_samples.device, dtype=original_samples.dtype)
-        self.timesteps = self.timesteps.to(original_samples.device)
+        dtype = torch.float32 if original_samples.device.type == "mps" else timesteps.dtype
+        self.timesteps = self.timesteps.to(original_samples.device, dtype=dtype)
         timesteps = timesteps.to(original_samples.device)
 
         schedule_timesteps = self.timesteps